Cellulose ester film is used in a liquid crystal displaying apparatus as a polarization plate protection film or a retardation film.
A melting production method using thermally melted cellulose ester is investigated for inhibiting the increasing of consumption of solvent accompanied with rapid raising of the demand of the film though the cellulose ester film is usually produced by a solution casting method.
In the melt-casting film formation, the melted cellulose ester having high viscosity is caste onto a cooling drum through a die; therefore the leveling of the cellulose ester is made insufficient and a problem such as that the fluctuation of the retardation tends to be caused and the optical property is inferior to that of the film produced by the solution cast method (cf. Patent Publications 1, 2 and 3).
Moreover, the cellulose ester film produced by melt-casting film forming method is large in variation of the retardation depending on the humidity variation and the bad influence of such the phenomenon is appeared as ununiformity of the image contrast when the film is used as the polarization plate protection film.
Patent Publication 1: WO92/05213
Patent Publication 2: JP-A 2000-352620
Patent Publication 3: JP-A 2003-270442